This invention relates generally to ozone testing, and in particular to a technique for continuously and accurately measuring the concentration of ozone dissolved in a liquid process stream.
Ozone is a triatomic form of oxygen which is produced by an electrical discharge through oxygen or by irradiation of oxygen by ultra-violet energy. At ordinary temperatures, ozone is highly unstable and quickly breaks down into a stable molecule of oxygen and a free oxygen atom. When this free atom of oxygen is blended with water, the water is converted to a peroxide valence which is a powerful oxidizing agent as well as a strong germicide.
Ozone is extensively used in the purification of drinking water, the treatment of sewage and industrial wastes, as well as in various chemical manufacturing processes. The unstable nature of ozone dictates its generation at the point of use, for it cannot be stored in containers in the manner of stable gases such as chlorine and oxygen.
While chlorination of water for purposes of sterilization is commonplace, in some instances chlorination is undesirable because of its influence on taste and flavor. Thus, in the making of beverages such as beer and soda, it is now the preferred practice to treat available water with ozone to ensure purity as well as flavor.
Ozone residual is the parts-per-million (ppm) of free ozone immediately available for reaction. To attain an effective germicidal action serving to destroy pathogens and all harmful bacteria and to react with oxidizable organic or inorganic chemical traces present in water, it is essential that the ozone concentration be in a predetermined range, such as 0.1 to 1 ppm. Below this range, the concentration is inadequate for its intended purpose, whereas an excessive concentration is wasteful. Moreover, since ozone is highly irritating and toxic even at low concentrations and is only slightly soluble in water, one must be careful to avoid introducing more ozone into the water than can be dissolved therein.
The standard laboratory technique for determining the concentration of ozone involves chemical analysis in a manual procedure which is time-consuming and at best produces only a spot check on concentration. It is known that dissolved ozone (O.sub.3) reacts quantitatively with potassium iodide at pH 9.5 or higher to liberate iodine in direct proportion to ozone concentration. Determination of ozone, using the iodide reaction, is the usual laboratory method, wherein the liberated iodine may be titrated amperometrically. Hence, in the standard method, by maintaining the necessary pH level and measuring the liberated iodine, one may arrive at the ozone concentration.